技术资料

Differences in ex vivo cell culture conditions can drastically affect stem cell physiology. We sought to establish an assay for measuring the effects of chemical,environmental,and genetic manipulations on the precision of repair at a single DNA double-strand break (DSB) in pluripotent and somatic human cells. DSBs in mammalian cells are primarily repaired by either homologous recombination (HR) or nonhomologous end-joining (NHEJ). For the most part,previous studies of DSB repair in human cells have utilized nonspecific clastogens like ionizing radiation,which are highly nonphysiologic,or assayed repair at randomly integrated reporters. Measuring repair after random integration is potentially confounded by locus-specific effects on the efficiency and precision of repair. We show that the frequency of HR at a single DSB differs up to 20-fold between otherwise isogenic human embryonic stem cells (hESCs) based on the site of the DSB within the genome. To overcome locus-specific effects on DSB repair,we used zinc finger nucleases to efficiently target a DSB repair reporter to a safe-harbor locus in hESCs and a panel of somatic human cell lines. We demonstrate that repair at a targeted DSB is highly precise in hESCs,compared to either the somatic human cells or murine embryonic stem cells. Differentiation of hESCs harboring the targeted reporter into astrocytes reduces both the efficiency and precision of repair. Thus,the phenotype of repair at a single DSB can differ based on either the site of damage within the genome or the stage of cellular differentiation. Our approach to single DSB analysis has broad utility for defining the effects of genetic and environmental modifications on repair precision in pluripotent cells and their differentiated progeny. View Publication

Src activation involves the coordinated regulation of positive and negative tyrosine phosphorylation sites. The mechanism whereby receptor tyrosine kinases,cytokine receptors,and integrins activate Src is not known. Here,we demonstrate that granulocyte colony-stimulating factor (G-CSF) activates Lyn,the predominant Src kinase in myeloid cells,through Gab2-mediated recruitment of Shp2. After G-CSF stimulation,Lyn dynamically associates with Gab2 in a spatiotemporal manner. The dephosphorylation of phospho-Lyn Tyr507 was abrogated in Shp2-deficient cells transfected with the G-CSF receptor but intact in cells expressing phosphatase-defective Shp2. Auto-phosphorylation of Lyn Tyr396 was impaired in cells treated with Gab2 siRNA. The constitutively activated Shp2E76A directed the dephosphorylation of phospho-Lyn Tyr507 in vitro. Tyr507 did not undergo dephosphorylation in G-CSF-stimulated cells expressing a mutant Gab2 unable to bind Shp2. We propose that Gab2 forms a complex with Lyn and after G-CSF stimulation,Gab2 recruits Shp2,which dephosphorylates phospho-Lyn Tyr507,leading to Lyn activation. View Publication

The WNT signaling pathway plays important roles in the self-renewal and differentiation of mesenchymal stem cells (MSCs). Little is known about WNT signaling in adipocyte differentiation of human MSCs. In this study,we tested the hypothesis that canonical and non-canonical WNTs differentially regulate in vitro adipocytogenesis in human MSCs. The expression of adipocyte gene PPARγ2,lipoprotein lipase,and adipsin increased during adipocytogenesis of hMSCs. Simultaneously,the expression of canonical WNT2,10B,13,and 14 decreased,whereas non-canonical WNT4 and 11 increased,and WNT5A was unchanged. A small molecule WNT mimetic,SB-216763,increased accumulation of β-catenin protein,inhibited induction of WNT4 and 11 and inhibited adipocytogenesis. In contrast,knockdown of β-catenin with siRNA resulted in spontaneous adipocytogenesis. These findings support the view that canonical WNT signaling inhibits and non-canonical WNT signaling promotes adipocytogenesis in adult human marrow-derived mesenchymal stem cells. View Publication

How HIV controllers (HICs) maintain undetectable viremia without therapy is unknown. The strong CD8(+) T-cell HIV suppressive capacity found in many,but not all,HICs may contribute to long-lasting viral control. However,other earlier defense mechanisms may be involved. Here,we examined intrinsic HIC cell resistance to HIV-1 infection. After in vitro challenge,monocyte-derived macrophages and anti-CD3-activated CD4(+) T cells from HICs showed low HIV-1 susceptibility. CD4 T-cell resistance was independent of HIV-1 coreceptors and affected also SIVmac infection. CD4(+) T cells from HICs expressed ex vivo higher levels of p21(Waf1/Cip1),which has been involved in the control of HIV-1 replication,than cells from control subjects. However,HIV restriction in anti-CD3-activated CD4(+) T cells and macrophages was not associated with p21 expression. Restriction inhibited accumulation of reverse transcripts,leading to reduction of HIV-1 integrated proviruses. The block could be overcome by high viral inocula,suggesting the action of a saturable mechanism. Importantly,cell-associated HIV-1 DNA load was extremely low in HICs and correlated with CD4(+) T-cell permissiveness to infection. These results point to a contribution of intrinsic cell resistance to the control of infection and the containment of viral reservoir in HICs. View Publication

Pluripotent stem cells,both human embryonic stem cells (hESC) and human-induced pluripotent stem cells (hiPSC),can give rise to multiple cell types and hence have tremendous potential for regenerative therapies. However,the tumorigenic potential of these cells remains a great concern,as reflected in the formation of teratomas by transplanted pluripotent cells. In clinical practice,most pluripotent cells will be differentiated into useful therapeutic cell types such as neuronal,cardiac,or endothelial cells prior to human transplantation,drastically reducing their tumorigenic potential. Our work investigated the extent to which these differentiated stem cell derivatives are truly devoid of oncogenic potential. In this study,we analyzed the gene expression patterns from three sets of hiPSC- and hESC-derivatives and the corresponding primary cells,and compared their transcriptomes with those of five different types of cancer. Our analysis revealed a significant gene expression overlap of the hiPSC- and hESC-derivatives with cancer,whereas the corresponding primary cells showed minimum overlap. Real-time quantitative PCR analysis of a set of cancer-related genes (selected on the basis of rigorous functional and pathway analyses) confirmed our results. Overall,our findings suggested that pluripotent stem cell derivatives may still bear oncogenic properties even after differentiation,and additional stringent functional assays to purify these cells should be done before they can be used for regenerative therapy. View Publication

Fbxo7 is an unusual F-box protein because most of its interacting proteins are not substrates for ubiquitin-mediated degradation. Fbxo7 directly binds p27 and Cdk6,enhances the level of cyclin D-Cdk6 complexes,and its overexpression causes Cdk6-dependent transformation of immortalised fibroblasts. Here,we test the ability of Fbxo7 to transform haematopoietic pro-B (Ba/F3) cells which,unexpectedly,it was unable to do despite high levels of Cdk6. Instead,reduction of Fbxo7 expression increased proliferation,decreased cell size and shortened G1 phase. Analysis of cell cycle regulators showed that cells had decreased levels of p27,and increased levels of S phase cyclins and Cdk2 activity. Also,Fbxo7 protein levels correlated inversely with those of CD43,suggesting direct regulation of its expression and,therefore,of B cell maturation. Alterations to Cdk6 protein levels did not affect the cell cycle,indicating that Cdk6 is neither rate-limiting nor essential in Ba/F3 cells; however,decreased expression of Cdk6 also enhanced levels of CD43,indicating that expression of CD43 is independent of cell cycle regulation. The physiological effect of reduced levels of Fbxo7 was assessed by creating a transgenic mouse with a LacZ insertion into the Fbxo7 locus. Homozygous Fbxo7(LacZ) mice showed significantly increased pro-B cell and pro-erythroblast populations,consistent with Fbxo7 having an anti-proliferative function and/or a role in promoting maturation of precursor cells. View Publication

It is known that umbilical cord blood (UCB) is a rich source of stem cells with practical and ethical advantages. Three important types of stem cells which can be harvested from umbilical cord blood and used in disease treatment are hematopoietic stem cells (HSCs),mesenchymal stem cells (MSCs) and endothelial progenitor cells (EPCs). Since these stem cells have shown enormous potential in regenerative medicine,numerous umbilical cord blood banks have been established. In this study,we examined the ability of banked UCB collected to produce three types of stem cells from the same samples with characteristics of HSCs,MSCs and EPCs. We were able to obtain homogeneous plastic rapidly-adherent cells (with characteristics of MSCs),slowly-adherent (with characteristics of EPCs) and non-adherent cells (with characteristics of HSCs) from the mononuclear cell fractions of cryopreserved UCB. Using a protocol of 48 h supernatant transferring,we successfully isolated MSCs which expressed CD13,CD44 and CD90 while CD34,CD45 and CD133 negative,had typical fibroblast-like shape,and was able to differentiate into adipocytes; EPCs which were CD34,and CD90 positive,CD13,CD44,CD45 and CD133 negative,adherent with cobble-like shape; HSCs which formed colonies when cultured in MethoCult medium. View Publication

Oligomerization is an important regulatory mechanism for many proteins,including oncoproteins and other pathogenic proteins. The oncoprotein Bcr-Abl relies on oligomerization via its coiled coil domain for its kinase activity,suggesting that a designed coiled coil domain with enhanced binding to Bcr-Abl and reduced self-oligomerization would be therapeutically useful. Key mutations in the coiled coil domain of Bcr-Abl were identified that reduce homo-oligomerization through intermolecular charge-charge repulsion yet increase interaction with the Bcr-Abl coiled coil through additional salt bridges,resulting in an enhanced ability to disrupt the oligomeric state of Bcr-Abl. The mutations were modeled computationally to optimize the design. Assays performed in vitro confirmed the validity and functionality of the optimal mutations,which were found to exhibit reduced homo-oligomerization and increased binding to the Bcr-Abl coiled coil domain. Introduction of the mutant coiled coil into K562 cells resulted in decreased phosphorylation of Bcr-Abl,reduced cell proliferation,and increased caspase-3/7 activity and DNA segmentation. Importantly,the mutant coiled coil domain was more efficacious than the wild type in all experiments performed. The improved inhibition of Bcr-Abl through oligomeric disruption resulting from this modified coiled coil domain represents a viable alternative to small molecule inhibitors for therapeutic intervention. View Publication

Procedures have been developed to label human erythropoietin (Ep) with biotin to detect and isolate the Ep-receptor. The labeling method used the abundant carbohydrate groups on Ep and resulted in biologically active biotin-Ep (b-Ep) containing 8 to 10 biotins per Ep molecule. Specific binding of b-Ep to cells from spleens of mice made anemic by phenylhydrazine injections was demonstrated using 125I-labeled streptavidin. B-Ep,together with fluorescently tagged streptavidin,was found to specifically detect Ep-receptor-bearing cells by flow cytometry. This was demonstrated in several ways. First,approximately 90% of nucleated spleen cells from phenylhydrazine-treated mice were clearly fluorescent after staining with b-Ep and streptavidin-phycoerythrin,whereas only background fluorescence was detected using spleen cells from untreated mice. In addition,Ep-receptors were detected on 5% to 10% of normal mouse bone marrow cells,and these cells could be identified as erythroid in nature by separating the cells into subpopulations based on light-scatter properties. Third,Ep-receptor expression was found to correlate positively with expression of transferrin receptors,confirming the erythroid nature of these cells. B-Ep was also used to isolate Ep-receptors from monkey COS cells transfected with the murine Ep-receptor cDNA. In these experiments a cell-surface-bound protein of approximately 65 Kd and an intracellular protein of approximately 60 Kd were isolated from these cells. The procedures described in this report for detecting Ep-receptor expressing cells and for isolating the Ep-receptor should be valuable for purifying erythroid cells from heterogeneous cell populations,for elucidating the structure of the Ep-receptor,and for studying the biological activities of Ep at the cellular and molecular level. View Publication

The mixed lineage leukemia (MLL) proto-oncogenic protein is a histone-lysine N-methyltransferase that is produced by proteolytic cleavage and self-association of the respective functionally distinct subunits (MLL(N) and MLL(C)) to form a holocomplex involved in epigenetic transcriptional regulation. On the basis of studies in Drosophila it has been suggested that the separated subunits might also have distinct functions. In this study,we used a genetically engineered mouse line that lacked MLL(C) to show that the MLL(N)-MLL(C) holocomplex is responsible for MLL functions in various developmental processes. The stability of MLL(N) is dependent on its intramolecular interaction with MLL(C),which is mediated through the first and fourth plant homeodomain (PHD) fingers (PHD1 and PHD4) and the phenylalanine/tyrosine-rich (FYRN) domain of MLL(N). Free MLL(N) is destroyed by a mechanism that targets the FYRN domain,whereas free MLL(C) is exported to the cytoplasm and degraded by the proteasome. PHD1 is encoded by an alternatively spliced exon that is occasionally deleted in T-cell leukemia,and its absence produces an MLL mutant protein that is deficient for holocomplex formation. Therefore,this should be a loss-of-function mutant allele,suggesting that the known tumor suppression role of MLL may also apply to the T-cell lineage. Our data demonstrate that the dissociated MLL subunits are subjected to distinct degradation pathways and thus not likely to have separate functions unless the degradation mechanisms are inhibited. View Publication

The mitochondrial contribution to the maintenance of human embryonic stem cell (hESC) pluripotency and culture homeostasis remains poorly understood. Here,we sought to determine whether hESC adaptation to different feeder-free culture conditions is linked to a mitochondrial adaptation. The expression of ESC pluripotency factors and parameters of mitochondrial contribution including mitochondrial membrane potential,mtDNA content,and the expression of master mitochondrial genes implicated in replication,transcription,and biogenesis were determined in 8 hESC lines maintained in 2 distinct human feeders-conditioned media (CM): human foreskin fibroblast-CM (HFF-CM) and mesenchymal stem cell-CM (MSC-CM). We show a robust parallel trend between the expression of ESC pluripotency factors and the mitochondrial contribution depending on the culture conditions employed to maintain the hESCs,with those in MSC-CM consistently displaying increased levels of pluripotency markers associated to an enhanced mitochondrial contribution. The differences in the mitochondrial status between hESCs maintained in MSC-CM versus HFF-CM respond to coordinated changes in mitochondrial gene expression and biogenesis. Importantly,the culture conditions determine the mitochondrial distribution within the stage-specific embryonic antigen 3 positive (SSEA3(+)) and negative (SSEA3(-)) isolated cell subsets. hESC colonies in MSC-CM display an intrinsic" high mitochondrial status which may suffice to support undifferentiated growth� View Publication

BACKGROUND Cell-based therapy shows promise in treating peripheral arterial disease (PAD); however,the optimal cell type and long-term efficacy are unknown. In this study,we identified a novel subpopulation of adult progenitor cells positive for CD34 and M-cadherin (CD34/M-cad BMCs) in mouse and human bone marrow. We also examined the long-lasting therapeutic efficacy of mouse CD34/M-cad BMCs in restoring blood flow and promoting vascularization in an atherosclerotic mouse model of PAD. METHODS AND FINDINGS Colony-forming cell assays and flow cytometry analysis showed that CD34/M-cad BMCs have hematopoietic progenitor properties. When delivered intra-arterially into the ischemic hindlimbs of ApoE/ mice,CD34/M-cad BMCs alleviated ischemia and significantly improved blood flow compared with CD34/M-cad BMCs,CD34/M-cad BMCs,or unselected BMCs. Significantly more arterioles were seen in CD34/M-cad cell-treated limbs than in any other treatment group 60 days after cell therapy. Furthermore,histologic assessment and morphometric analyses of hindlimbs treated with GFP CD34/M-cad cells showed that injected cells incorporated into solid tissue structures at 21 days. Confocal microscopic examination of GFP CD34/M-cad cell-treated ischemic legs followed by immunostaining indicated the vascular differentiation of CD34/M-cad progenitor cells. A cytokine antibody array revealed that CD34/M-cad cell-conditioned medium contained higher levels of cytokines in a unique pattern,including bFGF,CRG-2,EGF,Flt-3 ligand,IGF-1,SDF-1,and VEGFR-3,than did CD34/M-cad cell-conditioned medium. The proangiogenic cytokines secreted by CD34/M-cad cells induced oxygen- and nutrient-depleted endothelial cell sprouting significantly better than CD34/M-cad cells during hypoxia. CONCLUSION CD34/M-cad BMCs represent a new progenitor cell type that effectively alleviates hindlimb ischemia in ApoE/ mice by consistently improving blood flow and promoting arteriogenesis. Additionally,CD34/M-cad BMCs contribute to microvascular remodeling by differentiating into vascular cells and releasing proangiogenic cytokines and growth factors. View Publication